Field of the Invention
The present invention relates to a transmitter-receiver circuit and a method for distance measurement between a first node and a second node of a radio network.
Description of the Background Art
International Pat. Appl. No. WO 02/01247 A2, which corresponds to U.S. Publication No. 2003090365 discloses a method for measuring the distance between two objects with the use of electromagnetic waves. An interrogation signal of a base station and a response signal of a portable code emitter are transmitted twice at different carrier frequencies. The carrier frequencies in this case are correlated; i.e., they are dependent on one another. The carrier frequencies are approximated to one another, so that a phase shift between the signals can be measured. The distance of the code emitter to the base station is calculated from this phase shift. The interrogation signal and the response signal can be transmitted at different carrier frequencies or at the same carrier frequencies. The carrier frequencies are altered for a renewed interrogation/response dialog.
U.S. Pat. No. 6,731,908 B2 discloses a method for determining the distance between two objects for Bluetooth technology. In this case, the frequency is changed by frequency hops to measure a phase offset for multiple different frequencies. An object has a voltage-controlled crystal oscillator in a phase-locked loop (PLL), whereby the phase-locked loop is closed during the receiving and opened during the transmission, so that the receive signal and transmit signal have the same frequency. The phase of the local oscillator signal of the voltage-controlled crystal oscillator due to the synchronization by the PLL is thereby coherent to the received signal.
U.S. Pat. No. 5,220,332 discloses a distance measuring system which has an interrogator and a transponder and enables the nonsimultaneous measurement between two objects. A carrier signal is modulated with a (low-frequency) modulation signal with a variable modulation frequency to determine by a phase measurement or alternatively by a transit time measurement a distance between the interrogator and the transponder from the change in the modulation signal.